/*
 * Copyright 2002-2018 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      https://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.context.weaving;

import org.aspectj.weaver.loadtime.ClassPreProcessorAgentAdapter;
import org.springframework.beans.BeansException;
import org.springframework.beans.factory.BeanClassLoaderAware;
import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
import org.springframework.core.Ordered;
import org.springframework.instrument.classloading.InstrumentationLoadTimeWeaver;
import org.springframework.instrument.classloading.LoadTimeWeaver;
import org.springframework.lang.Nullable;

import java.lang.instrument.ClassFileTransformer;
import java.lang.instrument.IllegalClassFormatException;
import java.security.ProtectionDomain;

/**
 * Post-processor that registers AspectJ's
 * {@link org.aspectj.weaver.loadtime.ClassPreProcessorAgentAdapter}
 * with the Spring application context's default
 * {@link org.springframework.instrument.classloading.LoadTimeWeaver}.
 *
 * @author Juergen Hoeller
 * @author Ramnivas Laddad
 * @since 2.5
 */
public class AspectJWeavingEnabler implements BeanFactoryPostProcessor, BeanClassLoaderAware, LoadTimeWeaverAware, Ordered {

    /**
     * The {@code aop.xml} resource location.
     */
    public static final String ASPECTJ_AOP_XML_RESOURCE = "META-INF/aop.xml";


    @Nullable
    private ClassLoader beanClassLoader;

    @Nullable
    private LoadTimeWeaver loadTimeWeaver;


    @Override
    public void setBeanClassLoader(ClassLoader classLoader) {
        this.beanClassLoader = classLoader;
    }

    @Override
    public void setLoadTimeWeaver(LoadTimeWeaver loadTimeWeaver) {
        this.loadTimeWeaver = loadTimeWeaver;
    }

    @Override
    public int getOrder() {
        return HIGHEST_PRECEDENCE;
    }

    @Override
    public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
        enableAspectJWeaving(this.loadTimeWeaver, this.beanClassLoader);
    }


    /**
     * Enable AspectJ weaving with the given {@link LoadTimeWeaver}.
     * @param weaverToUse the LoadTimeWeaver to apply to (or {@code null} for a default weaver)
     * @param beanClassLoader the class loader to create a default weaver for (if necessary)
     */
    public static void enableAspectJWeaving(@Nullable LoadTimeWeaver weaverToUse, @Nullable ClassLoader beanClassLoader) {

        if (weaverToUse == null) {
            if (InstrumentationLoadTimeWeaver.isInstrumentationAvailable()) {
                weaverToUse = new InstrumentationLoadTimeWeaver(beanClassLoader);
            } else {
                throw new IllegalStateException("No LoadTimeWeaver available");
            }
        }
        weaverToUse.addTransformer(new AspectJClassBypassingClassFileTransformer(new ClassPreProcessorAgentAdapter()));
    }


    /**
     * ClassFileTransformer decorator that suppresses processing of AspectJ
     * classes in order to avoid potential LinkageErrors.
     * @see org.springframework.context.annotation.LoadTimeWeavingConfiguration
     */
    private static class AspectJClassBypassingClassFileTransformer implements ClassFileTransformer {

        private final ClassFileTransformer delegate;

        public AspectJClassBypassingClassFileTransformer(ClassFileTransformer delegate) {
            this.delegate = delegate;
        }

        @Override
        public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {

            if (className.startsWith("org.aspectj") || className.startsWith("org/aspectj")) {
                return classfileBuffer;
            }
            return  this.delegate.transform(loader, className, classBeingRedefined, protectionDomain, classfileBuffer);
        }
    }

}
